The invention relates to a parallel gripper having a housing and two adjustable base jaws which are slidably guided in the housing in a jaw guide opening, where the base jaws can be moved toward or away from each other by means of a wedge hook mechanism, and the wedge hook mechanism is adjustable by means of a piston which is guided in the housing.
Such parallel grippers are known. The two base jaws, on which extensions can be installed as gripper fingers, are often configured in known embodiments as a T-shape, when viewed in cross section and in the sliding direction, where the crossbar of the T-shape facing away from the workpiece is slidably, guided in a correspondingly configured jaw guide opening in the housing. There are also embodiments using rollers. In order to be able to generate high clamping forces and compensate for the concomitant rotational forces, the jaw guide has to be given a correspondingly large width, which means that the outside dimension of the base jaw, meaning the width in the direction of the transverse bar of the T-shape, must be made extremely large, compared with the width of the actual base body of the jaw. However, the result is that the width of the wedge hook connection, which is also described as the angular power transmission width and which is necessarily less than the width of the base body of the jaws, is likewise very small. This, in turn, mitigates against the transmission of high clamping forces.
Furthermore, every effort is made in the case of parallel grippers to keep the housing width as small as possible in order to reduce the required installation space. When the wall thickness of the housing is reduced, however, undesirable twisting and distortion occurs in the housing, undesirable with respect to the precision to be achieved, particularly when clamping forces are introduced and transmitted.
With this as the point of departure, the object of the present invention is to improve a parallel gripper of the type descried above so that, on the one hand, high clamping forces can be transmitted and absorbed, but the smallest possible overall installation space is utilized and, nonetheless, a high degree of precision is ensured during automation when using this parallel gripper.
In accordance with the invention, this object is accomplished with a parallel gripper in which the piston has an oval or substantially rectangularly configured shape with rounded corners and each base jaw has on both sides at least two guide ribs which are rectangular, wedge-shaped or trapezoidal extending in the direction of motion and the jaw guide opening has guide groove configured complementary thereto and the ratio of the housing wall thickness xe2x80x94measured between the root of the guide grooves and the outside of the housing xe2x80x94to the width of the housing xe2x80x94measured perpendicular to the direction of motion of the base jaws xe2x80x94is at least 0.2 and the ratio of the angular power transmission width of the wedge hook mechanism (width of the wedge hook) to the outside width of the base jaw is, at least 0.4
Through the combination of the preceding features, optimal utilization of the normally rectangular geometry of parallel gripper housings is achieved by the use of an oval or essentially rectangular piston in a generic parallel gripper. A greatest possible actuating force can be attained by utilizing the largest possible piston surface available. The piston is preferably operable hydraulically or pneumatically.
As a result of the base jaws each having at least two wedge-shaped or trapezoid-shaped guide ribs on both sides, the guide width achieved by these guide ribs in conjunction with the guide grooves can be increased in accordance with the number of guide ribs. So it is possible to realize a very small external width for the base jaw compared with bulkily configured broad T-guide grooves, or, expressed differently, the external width of the base jaw (measured from guide rib to guide rib) is only a very small amount larger than the width of the body of the base jaw or, expressed differently again, the width of the body of the base jaw is very large, compared with the external width of the base jaw, which in turn means that the angular power transmission width of the wedge hook connection, compared with the overall external width of the gripper base jaw, can be made very large. The great force from the oval or essentially rectangular piston can hereby be transferred to the gripper base jaws. The ratio of the width of the wedge hook to the external width of the base jaw is at least 0.4, preferably 0.5-0.7, and specifically 0.5-0.6.
As a further result of the ratio of the wall thickness of the housing to the total housing width being at least 0.2, preferably 0.23-0.3, and specifically 0.23-0.27, a stable design for the gripper housing is achieved, which can also sustain high rotational forces without distortion when gripping forces are transmitted and introduced.
Swiss patent 800 201 shows the use of several wedge-shaped guide ribs with jaw guides for centric chucks. The use of wedge hook mechanisms on parallel grippers is widely known. A proposal has also already been made to use oval actuating pistons in gripping devices.
With the present invention, a parallel gripper has been created which is compact overall, extremely stable and suitable for the transmission and absorption of high gripping forces and rotational moments.
In a preferred embodiment of the parallel gripper, the wedge hook mechanism has a wedge hook which is adjustable by means of the piston, the wedge hook engaging recesses running obliquely on both sides in the two base jaws.
The coupling between the piston and the wedge hook mechanism can be configured in any way. It has proved to be particularly advantageous if the wedge hook extends with a rod section through an opening in the housing in the bottom of the jaw guide opening into a cylinder, which is preferably formed by the housing body itself, and is connected there to the piston drive.
It also proves to be advantageous if the guide ribs are extended over the corresponding full length of each base jaw, not only to achieve the greatest possible guide width but also to achieve a great guide length, which specifically supports the absorption of rotational moments.
Furthermore, it is proposed that the ratio of the height of the guide ribs, which is measured as the amount the guide ribs protrude beyond the lateral surface of the body of the base jaws, to the width of the body of the base jaws (base width) be between 0.15 and 0.25, preferably between 0.19 and 0.24. To this extent, it is particularly recommended to provide three guide ribs located parallel one above the other, preferably over the entire length of the base jaw.
The angle of the flanks of the guide ribs is advantageously between 12xc2x0 and 20xc2x0, preferably between 14xc2x0 and 17xc2x0 to the normal direction of the guide ribs onto the lateral surface of the body of the base jaws.